BALI, Indonesia (CNN) -- In a dramatic reversal Saturday, the United States rejected and then accepted a compromise to set the stage for intense negotiations in the next two years aimed at reducing carbon dioxide emissions worldwide.

The White House, however, said in a statement that it still has "serious concerns" about the agreement.

"The negotiations must proceed on the view that the problem of climate change cannot be adequately addressed through commitments for emissions cuts by developed countries alone. Major developing economies must likewise act," the White House said.

Under the global warming pact, negotiating rounds would end in 2009.

The head of the U.S. delegation, Paula Dobriansky, undersecretary of state for democracy and global affairs, announced the United States was rejecting the plan. Her comments were met by booing from other delegations.

The White House said the negotiations must "clearly differentiate" and link responsibility with the level of emissions, size of the economy and energy use among developing countries.

"In our view, such smaller and less developed countries are entitled to receive more differentiated treatment so as to more truly reflect their special needs and circumstances," the statement said.

Rep. Edward J. Markey, D-Massachusetts, chairman of the House Select Committee on Energy Independence and Global Warming, called the compromise "a modest but important road map," and said the House committee would meet Wednesday to review the agreement.

The Saturday session, unpredictable and charged with emotion, was a roller coaster ride for delegates and the media.

After Dobriansky's announcement, a delegate from the developing country of Papua New Guinea challenged the United States to "either lead, follow or get out of the way."

Five minutes later, when it appeared the conference was on the brink of collapse, Dobriansky took the floor again to say the United States was willing to accept the arrangement. Applause erupted in the hall and a relative level of success for the conference appeared certain. Watch as emotional conference declared a success »

U.N. Secretary-General Ban Ki-moon called the pact "a good beginning."

"This is just a beginning and not an ending," Ban said. "We'll have to engage in many complex, difficult and long negotiations."

The U.N. climate change conference was to end Friday, but delegates returned to the negotiating table early Saturday after talks went well into the night before. The new pact is meant as a guide for more climate talks, which will culminate in Copenhagen in 2009.

Humberto Rosa, a Portuguese environmental official, said a standoff had come to an end when specific guidelines were removed from wording about future emission cuts.

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The United States objected to the specific guidelines, saying including them was moving the process too quickly and would preempt any future negotiations.

The European Union wanted an agreement to require developed countries to cut their emissions by 25 to 40 percent of 1990 levels by 2020. The United States, Japan and Canada oppose those targets.

The latest draft of the agreement removes the specific figures and instead, in a footnote, refers to the scientific study that supports them. Markey lambasted the Bush administration for initially opposing the guidelines, saying it was operating on "basis of denial and obfuscation."

"Not since Emperor Nero tried footnoting firefighting through more fervent fiddling have we seen such a transparently vain effort to avoid the inevitable," he said.

While the EU and the United States appeared to have ended their impasse, India raised objections to other parts of the agreement, notably the contributions developed nations would make to help developing nations clean up their emissions problems.

Environmental groups said the new pact makes the agreement less forceful than it might have been, but agreed that it is probably the best that could be had given the Bush administration's staunch objections.

Ban, who attended the conference earlier this week, but left for a visit to East Timor, announced Saturday he was unexpectedly returning to Bali to help shepherd the talks to a conclusion.

At one point Saturday, Ban took the podium to urge compromise.

"Frankly, I'm disappointed at the level of progress," he said.

Without specifics, however, some believed the final agreement would amount to failure.

"Let me underline once again that the Bali road map must have a clear destination," said Stavros Dimas, the EU environment commissioner.

But Rajendra Pachauri, who heads the U.N.'s Intergovernmental Panel on Climate Change, said such a stance would ignore the other progress being made at the conference. He said simply having a strong statement paving the way for future action would suffice.

"I wouldn't term that a failure at all," Pachauri said. "I think what would be a failure is not to provide a strong road map by which the world can move on, and I think that road map has to be specified with or without numbers. If we can come up with numbers, that's certainly substantial progress, and I hope that happens."

The U.N. Framework Convention on Climate Change passed the Kyoto Protocol 10 years ago, with the goal of limiting greenhouse gas concentrations in the atmosphere.

The United States was the only one among 175 parties -- including the European Union -- to reject it.E-mail to a friend